docs: Add `go install` as a first-class installation method

Start in the README installation section, where Docker and building from source are currently described. Add the provided go install command and local MCP client configuration as a first-class method; done means readers can install the binary without cloning or using Docker and configure it to run with stdio.

[!Note]
Responses generated with Claude

Problem

The README currently documents Docker/container as the primary installation method, with "Build from source" (go build) as a fallback framed as "If you don't have Docker." There's no mention of go install, which is the standard one-liner for installing Go binaries.

Proposed change

Add go install alongside the container option as a first-class installation method:

go install github.com/github/github-mcp-server/cmd/github-mcp-server@latest

Then configure the MCP client to use the local binary:

{
  "mcpServers": {
    "github": {
      "command": "github-mcp-server",
      "args": ["stdio"],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "<YOUR_TOKEN>"
      }
    }
  }
}

Why

• One command, no clone needed — go install fetches, builds, and places the binary in $GOPATH/bin in one step
• Faster startup — no container overhead on each MCP server launch
• No Docker/Podman dependency — many developers have Go installed but not a container runtime
• Lower resource usage — containerized MCP servers consume memory even when idle, limiting the number of IDEs or agent terminals that can run concurrently. A native binary uses no resources when not actively handling a request.
• Safe — the binary only makes outbound HTTP calls to the GitHub API via stdio; container isolation adds no meaningful security benefit here
• Standard Go practice — go install is the idiomatic way to distribute Go CLI tools

Verified

Tested on macOS (darwin/arm64):

$ go install github.com/github/github-mcp-server/cmd/github-mcp-server@latest
go: downloading github.com/github/github-mcp-server v1.0.1
$ github-mcp-server --version
GitHub MCP Server - Version: version